diff --git a/mm/swapfile.c b/mm/swapfile.c
index 74a1e324449d..ee515a6fbccd 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1443,8 +1443,10 @@ static bool swap_sync_discard(void)
 }
 
 static int swap_extend_table_alloc(struct swap_info_struct *si,
-				   struct swap_cluster_info *ci, gfp_t gfp)
+				   struct swap_cluster_info *ci,
+				   unsigned int ci_off, gfp_t gfp)
 {
+	int count;
 	void *table;
 
 	table = kzalloc(sizeof(ci->extend_table[0]) * SWAPFILE_CLUSTER, gfp);
@@ -1452,12 +1454,28 @@ static int swap_extend_table_alloc(struct swap_info_struct *si,
 		return -ENOMEM;
 
 	spin_lock(&ci->lock);
-	if (!ci->extend_table)
-		ci->extend_table = table;
-	else
-		kfree(table);
+	/*
+	 * Extend table allocation requires releasing ci lock first so it's
+	 * possible that the slot has been freed, no longer overflowed, or
+	 * a concurrent extend table allocation has already succeeded, so
+	 * the allocation is no longer needed.
+	 */
+	if (!cluster_table_is_alloced(ci))
+		goto out_free;
+	count = swp_tb_get_count(__swap_table_get(ci, ci_off));
+	if (count < (SWP_TB_COUNT_MAX - 1))
+		goto out_free;
+	if (ci->extend_table)
+		goto out_free;
+
+	ci->extend_table = table;
 	spin_unlock(&ci->lock);
 	return 0;
+
+out_free:
+	spin_unlock(&ci->lock);
+	kfree(table);
+	return 0;
 }
 
 int swap_retry_table_alloc(swp_entry_t entry, gfp_t gfp)
@@ -1472,7 +1490,7 @@ int swap_retry_table_alloc(swp_entry_t entry, gfp_t gfp)
 		return 0;
 
 	ci = __swap_offset_to_cluster(si, offset);
-	ret = swap_extend_table_alloc(si, ci, gfp);
+	ret = swap_extend_table_alloc(si, ci, swp_cluster_offset(entry), gfp);
 
 	put_swap_device(si);
 	return ret;
@@ -1519,13 +1537,21 @@ static void __swap_cluster_put_entry(struct swap_cluster_info *ci,
 		if (count == (SWP_TB_COUNT_MAX - 1)) {
 			ci->extend_table[ci_off] = 0;
 			__swap_table_set(ci, ci_off, __swp_tb_mk_count(swp_tb, count));
-			swap_extend_table_try_free(ci);
 		} else {
 			ci->extend_table[ci_off] = count;
 		}
 	} else {
 		__swap_table_set(ci, ci_off, __swp_tb_mk_count(swp_tb, --count));
 	}
+
+	/*
+	 * `SWP_TB_COUNT_MAX - 1` triggers extend table allocation. If the
+	 * count was above that, then the extend table is no longer needed,
+	 * so free it. And if we just put the count value from MAX - 1, it's
+	 * also possible that a pending dup just attached an extend table.
+	 */
+	if (unlikely(count == SWP_TB_COUNT_MAX - 2 || count == SWP_TB_COUNT_MAX - 1))
+		swap_extend_table_try_free(ci);
 }
 
 /**
@@ -1665,7 +1691,7 @@ static int swap_dup_entries_cluster(struct swap_info_struct *si,
 		if (unlikely(err)) {
 			if (err == -ENOMEM) {
 				spin_unlock(&ci->lock);
-				err = swap_extend_table_alloc(si, ci, GFP_ATOMIC);
+				err = swap_extend_table_alloc(si, ci, ci_off, GFP_ATOMIC);
 				spin_lock(&ci->lock);
 				if (!err)
 					goto restart;